In the 1960s, William H. Masters and Virginia Johnson began experimenting on the physiological changes that occur during sexual activities either conducted alone or with a partner. In 1966, their findings were published in their book, Human Sexual Response, detailing the first ever documented sexual response cycle (Mark, 2012). Even though this theory was later challenged due to various shortcomings, it is still the most commonly taught model on the subject.
The first stage of Masters and Johnson’s sexual response cycle is excitement or desire. Both males and females experience an increased heart rate, blood pressure, and breathing rate. Erect nipples may also appear (Kok, 2004). Vasocongestion or the sex flush also occurs in both males and females due to increase in blood pressure but it more noticeable during warm weather that when it is cold. In males, the excitement stage is characterized by the erection of the penis, enlargement, and elevation of testicles, and the contraction of the scrotal sack. The time it takes to erect the penis depends on age and the amount of stimulation the male receives. In females, the clitoris hardens, and the labia swell. Breasts enlarge, the vagina elongates, and its walls thicken (Mark, 2012; Kok, 2004).
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The plateau phase follows in this cycle. This is a period of sexual arousal before the sexual climax occurs. In both sexes, heart rate, blood pressure and breathing rate rises, sexual pleasure increases with stimulation, and they experience involuntary muscle tension. There is involuntary vocalizing as pleasure builds but when this stage is prolonged, it may result in frustration (Kok, 2004). In males, the coronal ridge expands, and the glans turns a purplish shade. The testicles also become further elevated in anticipation of ejaculation. Females experience intense vasocongestion in the vagina due to increased blood flow to the genitals, the vaginas expands, and the uterus becomes elevated (Kok, 2004). The clitoris retreats into the clitoral hood to avoid overstimulation, and the inner labia change color.
The orgasm stage follows, and it marks the sexual climax and the end of the plateau phase. Both males and females feel quick contractions of the pelvic muscles surrounding the genitals and anus. The heartbeat and breathing rate increase. Involuntary actions such as vocalizations, muscle spasms, and a general sense of euphoria are also characteristic of this phase (Mark, 2012). Males experience the intense urge to ejaculate due to the contraction of the internal sphincter of the bladder to prevent retrograde ejaculation, the vas deferens, prostate, and seminal vesicles. Semen is propelled out of the body through the urethra by relaxation of the external sphincter (Kok, 2004). The strength of these contractions and the volume of the semen determine the intensity of pleasure. In females, there are rhythmic contractions in the vaginal walls, anal sphincter, and uterus. The females also feel sexual pleasure which is subjectively located at different parts of their genitals.
The final phase is the resolution, which is a post-orgasm state when the body reverts to its normal state before arousal. In both sexes, the muscles relax, heart rate and breathing slow down, and blood pressure drops. The male penis becomes flaccid where age determines how fast this happens. In females, the nipples and breasts reduce in size. The clitoris returns to its normal position and the labia, uterus, and vagina return to their regular sizes. While this is a stage when males cannot have another orgasm, with further stimulation, females can experience multiple orgasms before resolution (Mark, 2012).
References
Kok, E. (2004). Differences between male and female sexual functioning. South African Family Practice , 46 (4), 12-15. doi:10.1080/20786204.2004.10873065
Mark, K. (2012, November 19). What we can learn from sexual response cycles. Psychology Today. Retrieved from https://www.psychologytoday.com/intl/blog/the-power-pleasure/201211/what-we-can-learn-sexual-response-cycles
